1. Field of the Invention
The present invention relates data storage devices, or disk drives, of the type that receive a removable disk cartridge. More particularly, the present invention relates to a read/write protect method for inhibiting unauthorized and/or inadvertent reading from, and writing to, a storage medium within a disk cartridge.
2. Description of the Prior Art
Removable disk cartridges for storing digital electronic information typically comprise an outer casing or shell that houses a rotatable storage medium, or disk, upon which electronic information can be stored.. The cartridge shell often comprises upper and lower halves that are joined together to house the disk. The disk is mounted on a hub that rotates freely within the cartridge. When the cartridge is inserted into a disk drive, a spindle motor in the drive engages with the disk hub in order to rotate the disk within the cartridge. The outer shell of the cartridge typically has some form of opening near its forward edge to provide the read/write heads of the drive with access to the recording surfaces of the disk. A shutter or door mechanism is often provided to cover the opening when the cartridge is not in use to prevent dust or other contaminants from entering the cartridge and settling on the recording surface of the disk.
Conventional 3.5" floppy disks have a mechanical slider mounted in a corner of the cartridge housing that can be moved from one position to another to indicate whether the floppy disk is, or is not, write-protected. An optical or mechanical switch in a floppy disk drive detects the position of the mechanical slider on the cartridge to determine whether the cartridge is write-protected. If so, the disk drive inhibits writing of information to the storage medium within the floppy disk cartridge. Unfortunately, the mechanical slider on the disk cartridge and the associated mechanical or optical switches in the disk drive increase the costs of the cartridge and drive. Moreover, there is no way to prevent a user from changing the write-protect status of the cartridge. All a user has to do is change the position of the mechanical slider. Another disadvantage of conventional 3.5" floppy disks and their associated drives is that there is no simple way to provide read protection in addition to the write protection. Data encryption can be applied to the recorded information, but data encryption techniques are highly complex and costly to implement.
Saldanha et al., U.S. Pat. No. 5,265,230, and Kulakowski et al., U.S. Pat. No. 5,132,954, disclose data storage systems in which at least a portion of a storage medium can be designated as "read only" by storing a unique data pattern in that portion of the storage medium. However, once a portion of the disk is designated as "read only", the "read only" state is permanent; a user cannot change the state of the "read only" portion of the storage medium.
Horiguchi, U.S. Pat. No. 5,311,498, discloses a method for password protecting one or more data blocks of an optical card. As Horiguchi describes, optical cards and disks are often used to store important information that may need to be protected from unauthorized reading. According to Horiguchi's data security method, at the time the important information is recorded on an optical card or disk, a password is stored in any data blocks that are to be protected from unauthorized reading. Only users who know the stored password can read the information in those data blocks. According to Horiguchi, the password protection is permanent. The password protection cannot be removed, even by a user that knows the current password. The current password also cannot be changed. These limitations are appropriate in Horiguchi's system, because the goal is data security. However, these limitations would be disadvantageous and unworkable in a more flexible read/write protection scheme of the type contemplated herein.
As the foregoing illustrates, there is a need for an improved read/write protection method for inhibiting unauthorized or inadvertent access to the storage medium of a disk cartridge. Preferably, the method would allow both write and read protection to be applied to the storage medium and would allow a user to change the protection mode of the storage medium, if desired. It would also be advantageous if a password could be used, when desired, to prevent unauthorized changes to the protection mode of the storage medium. Preferably, the method would not require additional mechanical or electrical components, nor any physical interaction with the housing of a disk cartridge. The present invention satisfies these needs.